I know this contradicts Tsunade's Necklace, but Sakura would become Hokage if they were just like the Sannin.
But Naruto's ability to wear Tsunade's necklace proves that he'll be Hokage.
So then who'd become Hokage?
I think that Naruto will be Hokage first, and then Sakura. There's nothing to prove this though.
Okay, there's one of my random thoughts. ^^